The present invention relates to a hand tool that is used to grip a workpiece and, more particularly, to such a tool that is self-adjusting.
Self-adjusting pliers are used to grip a workpiece with one hand, without the need to pre-adjust the pliers to accommodate the size of the workpiece. That is, the pliers automatically adjust to the size of the workpiece so long as the workpiece can fit between the jaws of the pliers. A type of self-adjusting pliers can be found in U.S. Pat. Nos. 4,651,598 (“598”), 4,662,252 and 5,351,584. As is described at column 1, lines 24 through 43 of 598, this type of pliers has first and second operating levers that define first and second jaws, respectively, which form one end of each lever. The remaining end of each lever defines a handle section. The handle sections can be manipulated with one hand to grip a workpiece of any size that fits between the jaws. One lever defines an elongated channel or slot having parallel opposed and interconnected side walls. One side wall of the channel defines a raceway and the other side wall defines a series of teeth. A pawl member is pivotally connected to the other lever and is confined within the elongated channel by a fastener that secures the levers together. A spring biased control arm interconnects the two levers intermediate their ends and continually urges one side of the pawl into contact with the raceway, which spaces the jaws and handle sections away from each other. The jaws move toward one another when the handle sections are squeezed together. When a workpiece is positioned between the jaws and the handle sections are squeezed together, the jaws will engage the workpiece and begin applying a limited force to the workpiece between the jaws. As the handle sections are squeezed together further, the control arm will move the pawl out of engagement with the raceway and, by a cam action, move it across the slot into engagement with the toothed surface of the slot, where the pawl is locked between two adjacent teeth of the toothed side wall of the slot. In this engaged position, the full force used to squeeze the handle sections together is effectively transferred to the jaws and amplified by simple leverage via the handle sections to allow the tool to grip the workpiece. Accordingly, the tool need not be adjusted to grip objects of different sizes.
As the user squeezes the handle sections of this type of tool together, the jaws pivot toward one another in “plier fashion.” That is, the movement of the jaws mimics the movement of the jaws of an ordinary pair of pliers in that the gripping faces of the jaws do not remain parallel to each other as they pivot. While this type of movement of the jaws is acceptable in situations where pliers are typically used, it is limiting in applications (for example, grasping flat or hex-shaped workpieces) in which the gripping faces of the jaws should remain parallel to each other. Spanners are typically used in these applications since the gripping faces of the jaws of a spanner are always parallel to each other as the jaws are moved toward each other to grasp the workpiece.
However, ordinary adjustable spanners are not self-adjusting. The jaws must be manually adjusted prior to gripping the workpiece to accommodate workpieces of different sizes. Typically, this adjustment is made by turning a threaded wheel that adjusts the distance between the gripping surfaces of the spanner, which makes conventional spanners somewhat awkward to use. More importantly, however, and unlike pliers, the jaws of a spanner cannot apply a levered force against a workpiece located between its jaws. Also, conventional adjustable spanners have fixed operating positions that require a clearance between the jaws of the spanner and the workpiece. In other words, the engagement between the jaws of the spanner and the workpiece is not tight. For example, the jaws of a spanner engage the corners of the head of a hex bolt, rather than the sides, which increases the possibility that the jaws will round off the corners of the hex bolt head under high torque loads.
Therefore, there is a need for a self-adjusting gripping tool that can apply a levered force against a workpiece that is located between its jaws, and that maintains a parallel relationship between the gripping faces of the jaws of the tool as the tool is operated.